The present invention generally relates to guidewires for use with medical catheters and to a welding procedure useful in manufacturing guidewires and other devices incorporating welding techniques. The welding procedure is particularly well-suited for assembling guidewire core wires of an alloy containing nickel and titanium as the principal components with a component such as a guidewire coil made of a different metal or material. Such an assembly procedure is in the nature of welding, and in the context of a medical guidewire, the weld forms the distal tip of the guidewire from the guidewire tip coil and the distal end of the core wire.
Guidewires have long been used in many medical procedures. Generally speaking, a guidewire is the initial member inserted into a body cavity during many transluminal procedures. A guidewire is an elongated fine wire device that is intended to readily pass through body passageways and to a location at which a medical procedure or treatment is to take place. Thereafter, in a typical arrangement, a catheter is slid over the thus inserted guidewire, with the catheter following the pathway defined by the guidewire. In general terms, a guidewire is flexible, at least at its remote distal end tip.
Remote distal end tip flexibility is often enhanced by providing a fine coil at the distal portion of the guidewire and securing that fine coil, typically at its distal end, to the distal end of the core wire of the guidewire. Typically, this securement application also includes a rounded distal tip that imparts some atraumatic characteristics to the guidewire. In the usual approach, these components are secured together by soldering, brazing, welding or by the use of an adhesive such as ultraviolet-curing adhesives or anaerobic adhesives such as cyanoacrylate adhesives.
It will be appreciated that core wires and guidewire coils are of extremely small diameter and are particularly fine and difficult to assemble by whatever means are utilized. Welding can be especially troublesome, particularly when attempting to work with certain materials that can be difficult to weld together. In this regard, it has been proposed to manufacture guidewires or other devices which incorporate components made of so-called shape memory alloys such as nickel and titanium alloys. Included are the so-called Nitinol alloys. Welding of these materials has met with considerable difficulty. Welding in accordance with conventional techniques has led to the development of embrittlement at the weld area, particularly of a Nitinol component. Materials such as Nitinol have been found to be so sensitive that they become embrittled when subjected to conditions that are too harsh.
It has been found that the procedure in accordance with the present invention provides welds of guidewires and other devices that minimize these types of embrittlement problems, even when a component being welded is made of a Nitinol material. In summary, the present invention accomplishes this improved welding by a procedure which includes inserting a guidewire coil or the like into a collet such that a distal end portion of the coil or the like projects out of the collet and beyond its face, and locating an elongated core wire or the like at a staged position remote from this face of the collet. Next, the projecting distal end portion of the coil is heated in order to form a heated tip mass until this mass engages the face of the collet, preferably in substantially sealed engagement. Then, this heated tip mass and the leading end of the core wire or the like are engaged with each other, typically by sliding the core wire or the like along the axis of the coil or the like and into the heated tip mass. Upon cooling, the leading end is joined to the now solidified coil tip mass so as to define a welded assembly. This welded assembly is suitable for use as a coil and core wire of a medical guidewire joined together by a generally atraumatic tip formed from the heated tip mass. This procedure and the products produced thereby are especially suitable for welding when one of the components, such as a core wire component, is made of a Nitinol alloy of which nickel and titanium are the principal components.
It is a general object of the present invention to provide an improved medical guidewire and welding process.
Another object of this invention is to provide an improved welding process, particularly suitable for medical devices, that avoids imparting harsh conditions to at least one of the components welded together, the procedure finding special application when one of the components is a Nitinol type of alloy.
Another object of the present invention is to provide an improved medical guidewire with a heat-formed distal tip having a core wire welded therewithin, which core wire is of a material that is particularly sensitive to deterioration when subjected to excessively high welding temperatures.
Another object of the present invention is to provide an improved process for manufacturing, including a procedure for welding a Nitinol elongated component together with another assembly component having a melting temperature greater than the Nitinol alloy.
These and other objects, features and advantages of this invention will be clearly understood through a consideration of the following detailed description.